Large chemical processing plants utilize a great many tube type heat exchangers which typically include bundles of heat exchange tubes whose ends are coupled to a header. To comply with stringent safety procedures and also for normal efficient operation, the header components of heat exchangers and tubes are periodically subjected to hydrostatic leak testing, at least twice, once after fabrication at the manufacturing site and secondly before plant startup in the field to ensure that the joints are free of defects and leakage. After the heat exchangers are tested and the results accepted, the heat exchangers are drained of water to ensure that internal header surfaces and tubes are dry. Drying may be done by hot air or inert gas. The purpose of internal surface drying is to prevent internal corrosion that might be caused after water testing during shipment and in standby operation mode. Such testing is necessary to avoid catastrophic joint leaks, and obviously to detect and correct or monitor even small leaks.
Conventional headers of air cooled heat exchangers are designed as closed boxes, each containing a plug sheet, tubesheet, end plates, top and bottom plate, nozzles, stiffeners and partition plates. Due to the complexity of air cooled heat exchanger headers which include corners and undercut regions, complete water draining and drying is not achieved with current drying procedures. Such accumulated moisture and water during shipment and in standby operation mode becomes stagnant and then corrosive, causing severe damage to internal parts of the headers and to adjacent parts of tubes coupled to the headers. Consequently, tube sheets and the heat exchange tubes themselves are at risk of damage which is not only expensive to repair, but causes shutdown of the whole heat exchanger. When such periodic inspection of headers results in repair or replacement and in many heat exchangers being taken out of line, costs in large chemical treatment plants can have production losses reaching $300,000 per day due to downtime.
The present invention addresses this severe problem with a new design for headers intended to extend equipment cycle life and prevent unexpected failures due to corrosion.